1. Field of the Invention
The present invention relates to a clamped cutting tool used in the metalworking field. More, specifically, it relates to improvements in a clamped cutting tool for firmly holding a cutting insert and a shim member which is laid under the cutting insert.
2. Prior Art
FIGS. 1 through 4 depict a conventional clamped cutting tool which comprises a point-center bent tool-holder 20, right handed, including a forward end portion 24. A recess 30 with a generally rhombic shaped bottom face is formed in an upper surface of the forward end portion 24 and a cutting insert 32 of a rhombic shape is received in the recess 30 with a rhombic shim member 34 interposed therebetween. The bottom wall of the recess 30 is parallel to the upper surface of the forward end portion 24. The side walls of the recess 30, each of which is vertically upwardly extending from the bottom wall, have upper walls 54 at the level of the cutting insert 32 and lower walls 56 at the level of the rhombic shim member 34. The upper walls 54 slightly project from the lower walls 56. The recess 30 has a hole 36 of which the center axis is perpendicular to the bottom wall of the recess 30. The shim member 34 which may be made of steel or cemented carbide also has a hole 38 which is eccentric to the hole 36. Above the hole 38, the shim member 34 includes a bore 40 which has a larger diameter than the hole 38, and is concentric to the hole 38, but is at the center of the shim member 34. The cutting insert 32 has an aperture 42 at the center thereof, of which the diameter is smaller than that of the bore 40.
The cutting insert 32 is secured to the recess 30 in the following manner by a locking pin 44. The locking pin 44 consists of a large diameter rod portion 46, a flange portion 48 which is eccentric to the large diameter rod portion 46, a neck portion 50, and a head portion 52. Both the neck and head portions 50 and 52 are concentric to the flange portion 48. The flange portion 48 has a diameter which is approximately the same as that of the bore 40. The large diameter rod portion 46 of the locking pin 44 is downwardly inserted into the holes 36 and 38.
The reason why the flange and head portions 48 and 52 are made concentric is so that the bore 40 engaging with the flange portion 48 is located at the center of the shim member 34, and the aperture 42 engaging with the head portion 52 is located at the center of the cutting insert 32. Therefore the cutting insert 32 and shim member 34 can be symmetrical and consequently the tool-holder mechanism can be applied to both point center bent tools, right handed and left handed.
The cutting insert 32 is mounted on the shim member 34 in such a manner as to be tightly fastened between the head portion 52 of the locking pin 44 and the side walls 54 of the recess 30. The shim member 34 is also fastened between the flange portion 48 and the side walls 56 of the recess 30. Because the locking pin 44 is rotatable about the axis of the hole 36, the cutting insert 32 and shim member 34 can be mounted on and removed from the recess 30. The locking pin 44 has a regular-hexagonal socket (not shown) at the bottom end surface 58 thereof, to be rotated with a hexagonal wrench.
The reason why the side walls of the recess 30 include the upper projected walls 54 is as follows. Since the flange and head portions 48 and 52 of the locking pin 44 are concentric to each other and eccentric to the large diameter rod portion 46, the shim member 34 and the cutting insert 32, which are retained by the flange portion 48 and the head portion 52 respectively, move with the rotation of the locking pin 44. If the shim member 34 contacts with the side walls 56 before the cutting insert 32 contacts the side walls 54, only the shim member 34 is substantially fastened nevertheless the cutting insert 32 is not tightly fastened. Hence, the upper side walls 54 project from the lower side walls 56, thereby providing a clearance "C" between the walls 54 and 56.
With the above construction, the clamped cutting tool, however, has the problems caused by the clearance "C". More specifically, the shim member 34 can not be tightly fastened between the side walls 56 and the flange portion 48 while the cutting insert 32 is tightly mounted. The shim member 34 may sometimes shake or budge on the recess 30 as shown by a two-dash-dot-line in FIG. 4, during the cutting operation. In case that the shaking or budging increases, the shim member 34 impacts upon the work piece, thereby interrupting stable cutting operations.
Referring now to FIG. 5, another conventional clamped cutting tool is described. In the tool, the side walls 60 of the recess 30 do not have projection or clearance, but are simply vertically extending from the bottom wall thereof.
A mechanism for preventing the locking pin 44 from coming out when fastening the pin with the hexagon wrench is provided near the locking pin 44. More specifically, at the lower portion of the hole 36 is formed a larger diameter bore 62 which is concentric with the hole 36. The locking pin 44 has a circular groove 64 of which width is adequate to be accepted to the bore 62. Around the circular groove 64 is engaged a C-formed retaining ring 66 which is received in the bore 62, so that the locking pin 44 can be firmly locked at the hole 36.
In constructing the clamped cutting tool, after inserting the locking pin 44 into the bore 40 and holes 38 and 36, the locking pin 44 is further downwardly advanced, thereby the lower end thereof is slightly projected from the lower surface of the forward end portion 24. Next, the C-shaped ring 66 is engaged with the circular groove 64. The locking pin 44 is then upwardly thrusted to be positioned to the original location, so that the C-shaped ring 66 is received into the bore 62.
However, the clamped cutting tool has the following problems caused by the circular groove 64 and the bore 62. Due to the provision of the bore 62, a length ".lambda." of the locking pin 44 which contacts the inner peripheral surface of the hole 36 is shortened. A moment resulting from a resistance force "F" that is produced by action against the cutting insert 32 is received by the shortened length defined by ".lambda.". Therefore, a resistance force of the tool-holder 20 against the moment is reduced. Especially, if the distance "H" of the forward end portion 24 is small, the tool-holder 20 can not provide sufficient holding force for the cutting insert 32.